The
Problem:In 1813 Benjamin
Heyne wrote the following letter to the Linnean Society.

Dear
Sir:I had an opportunity some time ago of
mentioning to you a remarkable deoxidation of the leaves of a plant in
day-light.As the circumstance is in itself curious, and throws great
light on the opinion of those celebrated philosophers who have written on the
subject, I will state it shortly in this letter, which if you please, you may in
extract, or in any way you think proper, lay before the Society.The leaves of the Cotyledon calycina, the plant called by Mr. Salisbury
Bryophyllum calycinum, which on the whole have an herbaceous taste, are in the
morning as acid as sorrel, if not more so.As the day advances, they lose their acidity, and are tasteless about
noon; and become almost bitterish towards evening.This is the case in India, where this plant is pretty generally
cultivated in our gardens and it remains to be seen if the same takes place in
the hot-houses in England, where it has been lately introduced.

Case
Study:

Leaves
were removed in the morning (about 7:30 am) and late afternoon (about 4:00
pm) from the leaves of two species of Bryophyllum, also called Mother
of Thousands.Break open a leaf
and touch it lightly to your tongue for a quick taste.Can you tell which leaf was collected in the morning and which in the
evening?

Now,
write a letter to Mr. Heyne describing our current scientific understanding
for the observations described in his letter.

Reference:

Thanks to Dr. David Walker
(http://www.daw.exl.co.uk/) for sharing the letter with the Plant Ed
ListServe.